This invention relates generally to an electrostatographic printing machine, and more particularly concerns an improved toner dispensing apparatus for use therein.
Electrostatographic printing includes electrographic printing and electrophotographic printing. In both of these processes, an electrostatic latent image is recorded corresponding to the original document to be reproduced. This is achieved in electrophotography by charging a photosensitive element having a photoconductive insulating layer to a substantially uniform potential. The charged photoconductive surface is exposed to a light image of the original document. As a consequence of the exposure, the charge is selectively dissipated in the irradiated areas in accordance with the light intensity reaching the photoconductive surface to create an electrostatic latent image thereon. Electrographic printing differs from electrophotographic printing in that the electrostatic latent image is created without the use of photosensitve materials. That is, electrophotography requires the use of a suitable photoconductor whereas electrography does not.
Development of the electrostatic latent image, in electrophotography and electrography, is accomplished by contacting the latent image with a developer mix. Typical developer mixes generally comprise dyed or colored thermoplastic particles, known in the art as toner particles, mixed with carrier granules, such as ferromagnetic granules. The toner particles and carrier granules are triboelectrically attracted to one another such that the tone particles adhere to the outer surface of the carrier granules. As the developer mix contacts the latent image, the greater attractive forces produced thereby casue the transfer and adherence thereto of the toner particles in image configuration.
It is apparent that during the development cycle, the toner particles are depleted from the developer mix. As the toner particles in the developer mix are depleted, during the development of the latent image, additional toner particles must be furnished thereto to maintain copy density at a desirable level. Hence, in order to produce an efficient printing machine, it is necessary to conveniently and effectively replenish the toner particles used in the formation of copies. Hereinbefore, predetermined amounts of toner particles were added periodically to the developer mix. This was achieved by the operator manually adding toner particles to the mix, or by a dispenser discharging fixed amounts of particles in the mix at specific time intervals. The particle dispensers heretofore utilized frequently metered incorrect amounts of toner particles into the developer mix. Thus, if the percentage of toner particles in the developer mix were too small, the copy density would be too low and contrast disappears, whereas if the percentage of toner particles in the developer mix were too great, copies would be smudged.
Accordingly, it is a primary object of the present invention to improve dispensing of toner particles into the developer mix of an electrostatographic printing machine.